There exist related-art four-way cassette-type indoor units that can be ceiling mounted in air-conditioned spaces. Such indoor units have a structure in which, for example, an outer peripheral portion (laterally side portions) of an air-sending device such as a turbofan is surrounded by heat exchanger. The air-sending device sucks air from below and laterally blows the sucked air so that the air is air-conditioned by passing through the heat exchanger, and the air-conditioned air is blown to the air-conditioned space. In the heat exchanger of such an indoor unit, headers are disposed at upper and lower positions, a plurality of flat tubes are arranged in the up-down direction (vertical direction) between the headers, and corrugated fins are disposed between the flat tubes (see, for example, Patent Literature 1).